wireshark-dev August 2010 archive
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wireshark-dev: Re: [Wireshark-dev] independent dissection of plu

Re: [Wireshark-dev] independent dissection of plug-ins

From: Guy Harris <guy_at_nospam>
Date: Tue Aug 31 2010 - 07:04:24 GMT
To: Developer support list for Wireshark <wireshark-dev@wireshark.org>

On Aug 30, 2010, at 11:14 PM, upendra.allu@wipro.com wrote:

> Is It that one pcap file only supports only one DLT?

Yes.

If you have a sufficiently recent version of libpcap on your machine, "man pcap-savefile" will describe the pcap format; you can also see it described at

        http://wiki.wireshark.org/FileFormatReference/libpcap

In both of those places you can see that a pcap file has only one file header, and the DLT value is in the file header, so there's only one DLT value in a pcap file, so a pcap file, by definition, supports only one DLT.

> If yes what is the best way to meet my requirement? I want to decode multiple plug-ins in the same pcap file (without decoding the plug-ins complete stack)

You would have to define a pseudo-protocol that includes a field that indicates which plugin to call, and put a pseudo-link-layer header with that field in front of your plugin's data, and then use a single DLT for that pseudo-protocol.

(Wireshark was designed to support protocols on a network, not arbitrary artificial file formats. Attempts to do something outside what it was designed for might work, but they aren't going to be as simple as you'd like.)
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